1. Field of the Invention
The present invention generally relates to a microwave integrated circuit (MIC), and more particularly to a triple-band gain amplifier capable of simultaneously operating in three separated frequency bands.
2. Description of the Related Art
The rapid development of the coexist operation of multi-standard wireless and mobile communication has been driving RF transceivers to have a new multi-band characteristic. Existing examples include the multimode wireless LAN IEEE802.11a/b/g card (at 2.4 GHz and 5.2 GHz), the integrated Bluetooth and wireless LAN card (at 2.4 GHz, 5.2 GHz), and the integrated GSM/WLAN handset (900 MHz, 1900 MHz, and 2.4 GHz). The new wireless standard Ultra-Wide-Band system (UWB), allocated from 3.1–10.6 GHz, is soon to be in service. This requirement has driven the conventional single-band RF circuits, such as gain amplifier (GA), bandpass filter, mixers, voltage controlled oscillators (VCOs) and power amplifier (PA), to a new design era.
To have gain at multiple frequency bands, a prioi-art design by S. Wu and B. Razavi, entitled “A 900-MHz/1.8-GHz CMOS receiver for dual-band applications,” IEEE J. Solid-State Circuits, vol. 33, pp. 2178–2185, December 1998, was implementing two LNA circuits separately, one for the low-band (800–1000 MHz) and the other for the high-band 1800 MHz. Other design by J. Ryynanen et al, entitled “A dual-band RF front-end for WCDMA and GSM applications,” IEEE Journal of Solid-State Circuits, vol. 36, August 2001, adopted a switched dual-band architecture, where two variable-gain LNAs at 900 MHz and 2100 MHz respectively are switched them by biasing the cascaded transistors. This approach needs more component count since one gain amplifer is unused when the other is activated.
Wideband design, such as the work by Armiji and Meyer, entitled “A new wide-band Darlington amplifier,” IEEE J. Solid-State Circuits, vol. 16, p. 634, December 1981, seems to be able to use simpler circuit architecture and fewer components to achieve gain over a broad range of frequency. But it has drawback of in-band interference problem.
The third approach, proposed by H. Hashemi and A. Hajimiri, entitled “Concurrent Multiband Low-Noise Amplifiers-Theory, Design, and Applications,” IEEE Trans. Microwave Theory Tech., Vol. 50, No. 1, pp. 288–301, January 2002, employed dual-band match technique to achieve gain match simultaneously at two different frequency bands. This results in high reuse of passive and active components. This design is limited to dual-band applications.
According to the above problems, there is a need for a highly-reused gain-amplifier circuit, capable of achieving gain match simultaneously at three different frequency bands for the rapidly-developed multi-mode wireless communications.